Navy Yard Shooting Timeline

On the morning of Sept. 16, a Navy defense contractor carried out a bloody attack in the heart of the nation's capital, killing 12 civilians and wounding more than a dozen others.

In the ensuing chaos, authorities swept the 41-acre Washington Navy Yard, looking for not one, but three suspects, and tried to account for more than 18,000 people who work on the premises. At the end of the day, they had one suspect: Aaron Alexis, 34. He was killed by security forces at the scene.

The Huffington Post has compiled a timeline from stories, tweets and press releases filed during the pandemonium:

The Shooting

Just before 8:15 a.m., Alexis carried a shotgun into Building 197, the headquarters for Naval Sea Systems Command, which hires contractors to build and maintain ships and submarines. Alexis reportedly had security clearance to enter the building through his employer, Hewlett-Packard.

At some point, he may have picked up a handgun after the shooting began, the FBI reported on Tuesday.

Between 8:15 and 8:20 a.m., police started receiving calls about gunfire.

Response And Injuries

Within two or three minutes, Metropolitan Police officers were on the scene, Police Chief Cathy Lanier said during a press conference. They identified Alexis as a suspect immediately, and started engaging him.

Several victims had already been identified, including a wounded police officer and Navy Yard security officer.

At about 8:35 a.m., police identified two other men, one carrying a handgun and the other carrying a rifle, who they thought might be a second and third shooter, according to the Orlando Sentinel. They continued to look for the two other suspects for several hours. Authorities now believe that Alexis was the sole person responsible for the attack.

Police exchanged gunfire with Alexis in a battle that lasted more than 30 minutes.

Editor's Note: At a press conference Tuesday, an FBI representative clarified that Alexis had a shotgun when he entered Building 197. That contradicts earlier reports that he entered with three weapons.

UNKNOWN, UNSPECIFIED - SEPTEMBER 16: In this handout photo provided by the FBI, Aaron Alexis is shown in a photo prior to the mass shooting at the Washington Navy Yard on September 16, 2013 in Washington, D.C. Authorities believe Alexis was a gunman involved in the shootings at the Navy Yard, where at least 12 people were shot and killed. (Photo by FBI via Getty Images)